BRATTLEBORO — The state permit that allows Entergy Nuclear to dump 543 million gallons of hot water into the Connecticut River every day expired six years ago in 2006, but there’s a good reason for that.

Catherine Gjessing, associate general counsel of the Department of Environment Conservation, said the permit itself is 11 years old, and is based in some instances on much older science and technology, in one case 34 years old.

Gjessing updated the status of the permit to members of the Vermont State Nuclear Advisory Panel and about two dozen area residents at a meeting held at Brattleboro Union High School on Thursday.

Gjessing said the federal Environmental Protection Agency was rewriting the regulations that deal with the discharges, and the underlying science, and the state was forced to wait for its federal counterparts. The new regulations call for “best available technology.”

Gjessing said that the “protracted federal litigation” was supposed to result in draft rules by 2011, but by August 2012, they still weren’t released, so the state is pushing ahead.

Entergy had applied in advance of its permit expiring, Gjessing said, so the old permit is still in force.

The permit, the national pollutant discharge elimination system permit, does view heat as a pollutant, Gjessing told the group.

Under the terms of the Vermont permit, all that 100-degree water can’t raise the Connecticut River more than 1 degree Fahrenheit, she said.

That measurement is made 1½ miles downstream from the Vernon reactor.

One major issue under consideration for the new permit is the use of Vermont Yankee’s cooling towers, as the plant hasn’t used its cooling towers year-round since 1978, using Connecticut River water instead, and saving a lot of electricity in the process.

Critics of Yankee, including the Connecticut River Watershed Council, wants the plant to switch to all-cooling tower operation, or closed cycle, and thus eliminate the use of the river water in cooling the reactor and its cooling systems. Earlier this summer, Yankee was forced to reduce power because of the low flows in the river, and the high temperature of the river.

“Closed cycle takes a fair amount of power,” Elizabeth Miller, commissioner of the Department of Public Service, chairwoman of VSNAP, told the group.

Gjessing said the current permit has been litigated by state environmental groups, first in Windham Superior Court in Newfane, and all the way to the Vermont Supreme Court, which in 2009 upheld the permit. Environmental groups claimed the hot water discharge was having an adverse effect on the river’s cold-water habitat fish, such as shad and salmon.

But Gjessing said the years of waiting are over, and the state is gearing up to write the permit and is hiring experts to analyze scientific reports submitted by the Connecticut River Watershed Council since the state was “unable to verify” the council’s claims on their own.

She said the Department of Environmental Commission was creating a website devoted to the water discharge permit issue.

Gjessing said that the 543 million gallons was “a very small fraction” of the daily flow of the Connecticut River.

Anti-nuclear activist Sally Shaw of Massachusetts, who said she lives 4 miles downstream from Yankee, said that even the U.S. Fish and Wildlife Service, years earlier in comments about Yankee’s proposed power boost, had raised questions about additional discharge.

“We will be looking at these issues. We’re taking them seriously,” Gjessing said.

But the state doesn’t have the expertise to evaluate these issues, and will have to hire or bring in experts, she said.